1. Field of the Invention
The present invention relates to a bidirectional signal transmission circuit which can be applied to a drive circuit for an active matrix display having an image reversing function. More particularly, the present invention relates to a technology for reducing noise generated in a bidirectional signal transmission circuit.
2. Description of the Related Art
Active matrix displays each having a scan drive circuit using polycrystalline silicon thin film transistors are typified by liquid crystal displays and organic electroluminescent displays. For the liquid crystal display used in, for example, a camcorder or an information portable terminal, in order to support an application for displaying an image on a rotatable monitor, the display uses a scan drive circuit having a lateral reversing function and a longitudinal reversing function. In other words, the display has a bidirectional scan drive circuit therein. The size of the display is recently being increased. Following the increase of the size thereof, an approach of connecting display panels to constitute a large screen is known. For example, in a case where four display panels constitute one large screen and the display panels having the same structure are arranged in each diagonal line, one of the display panels is rotated by 180 degrees and is disposed. In order to uniform the scanning direction of an image to be displayed, each display panel needs to have a bidirectional scan drive circuit therein. A bidirectional signal transmission circuit constitutes the principal part of the bidirectional scan drive circuit. For example, Japanese Unexamined Patent Application Publication Nos. 7-13513, 7-146462, 8-55493, 8-79663, 8-106795, 11-176186, and 11-305742 disclose known arts.
In a known bidirectional signal transmission circuit, a signal supplied from the exterior of this circuit is sequentially transmitted from one end to the other end of the circuit. In order to confirm the sequential transmission at the exterior of the circuit, the transmitted signal is output. The signal transmitting direction is changeable between both the ends of the circuit in response to a switching signal which is supplied from the exterior. The known bidirectional signal transmission circuit utilizes a layout design to reduce the number of terminals connected to the outside as much as possible. Specifically, in the layout design, a signal line disposed between input terminals in both the ends of the bidirectional signal transmission circuit is parallel to a signal line arranged between output terminals in these ends. In order to reduce the number of terminals as mentioned above, each line connecting the terminals in these ends of the bidirectional signal transmission circuit is long and has high resistance. Therefore, a steep change in potential of a signal line causes noise on the adjacent signal line. The noise triggers a malfunction in the bidirectional signal transmission circuit.